Internal combustion engines may be downsized to improve fuel economy. In order to achieve high engine peak power, turbochargers may be utilized to increase boost pressure. In one example, a turbocharger may include a compressor and a turbine connected by a drive shaft, where the turbine is coupled to an exhaust manifold side of the engine, and the compressor is coupled to an intake manifold side of the engine. A throttle may be positioned between the compressor and the intake manifold for controlling airflow into the engine intake manifold. The boost pressure may be controlled by adjusting the amount of exhaust gas reaching the turbine, for example with a wastegate. In response to a torque demand, an engine control system may compute a desired throttle inlet pressure and send it to the wastegate feedback controller. Within the wastegate feedback controller, a wastegate command may be generated to actuate the wastegate. In an example, the wastegate feedback controller may be a proportional-integral-derivative (PID) controller with feedforward action. Gains of the proportional, integral, and derivative term of the PID controller need to be tuned for the engine system. However, determining the gains of the PID controller may be an arduous task because controller gains depend on the operating conditions such as air flow through the engine, turbine speed, and barometric pressure.
Other attempts to determine PID controller gain include tuning the controller through relay feedback. One example approach is shown by Boiko et al. in U.S. Pat. No. 8,255,066B2. Therein, oscillations corresponding to a selected gain or phase margin are generated, and PID controller tuning parameters are computed based on the amplitude and frequency of the oscillations. Further, the prior art's method is “non-parametric” because it does not attempt to estimate any plant (process) model parameters.
However, the inventors herein have recognized the above issues as well as other potential issues with such systems. As one example, the procedure for determining PID tuning parameters is complicated and may be time consuming and do not provide a straightforward approach to trading off speed of response and robustness. Further, controller parameters may need to be updated during extensive vehicle calibration process to account for late hardware changes or part-to-part variability or after the original in-factory calibration due to system degradation over time.
In one example, the issues described above may be addressed by a method for an engine system, comprising: during steady engine operation, inducing a boost pressure oscillation by actuating a wastegate, and compensating a manifold air pressure with a corresponding throttle oscillation; and updating a gain of a wastegate feedback controller based on the boost pressure oscillation. For example, the gains may be updated during engine operation based on parameters describing the measured boost pressure oscillation, such as amplitude, frequency, etc. In this way, the gain of the wastegate feedback controller may be updated online while the engine is running.
As one example, a wastegate may be controlled by a wastegate feedback controller in the form of a PID controller. During steady engine operation, a boost pressure oscillation of small amplitude may be induced by oscillating a wastegate position. The boost pressure may be a throttle input pressure or a compressor outlet pressure. For a diesel engine, the boost pressure may be the intake manifold pressure. As a non-limiting example, the boost pressure is herein referred to as a throttle input pressure (TIP). In response to the TIP oscillation, a throttle may be oscillated to maintain a constant manifold air pressure. In another embodiment, in hybrid applications, the electric motor or a generator might be used to suppress the impact of throttle inlet pressure oscillations on torque output. PID controller gains may be updated as a mathematical function of the frequency, amplitude, and phase of the boost pressure oscillation. By updating the wastegate feedback controller gain over time, boost pressure may be robustly controlled with tolerance for vehicle component degradation. By determining the gain of the wastegate feedback controller during steady engine operation, wastegate feedback controller gain may be updated with reduced interruption to engine operation.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.